1. Field of Invention
This invention relates generally to a fluid ejector apparatus.
2. Description of Related Art
Fluid ejector systems, such as drop-on-demand liquid ink printers, such as piezoelectric, acoustic, phase change wax-based or thermal, have at least one fluid ejector from which droplets of fluid are ejected towards a receiving sheet. Within the fluid ejector, the fluid is contained in a plurality of channels. Power pulses cause the droplets of fluid to be expelled as required from orifices or nozzles at the end of the channels.
In a thermal fluid ejection system, the power pulse is usually produced by a heater transducer or resistor, typically associated with one of the channels. Each resistor is individually addressable to heat and vaporize fluid in one of the channels. As voltage is applied across a selected heater resistor, a vapor bubble grows in the associated channel and displaces ink from the channel, so that it is ejected from the channel orifice as a droplet. When the fluid droplet hits the receiving medium, the fluid droplet forms a dot or spot of fluid on the receiving medium. The channel is then refilled by capillary action, which, in turn, draws fluid from a supply container of fluid.
A fluid ejector system can include one or more thermal fluid ejector dies having a heater portion and a channel portion. The channel portion includes an array of fluid channels that bring fluid into contact with the resistive heaters, which are correspondingly arranged on the heater portion. In addition, the heater portion may also have integrated addressing electronics and driver transistors. Since the array of channels in a single die assembly is not sufficient to cover the length of a page, the fluid ejector is either scanned across the page with the receiving medium advanced between scans or multiple die assemblies are butted together to produce a full-width fluid ejector.
Because thermal fluid ejector nozzles typically produce spots or dots of a single size, high quality fluid ejection requires the fluid channels and corresponding heaters to be fabricated at a high resolution, such as, for example, on the order of 400-600 or more channels per inch.
When the fluid ejector is an ink jet printhead, the fluid ejector may be incorporated into for example, a carriage-type printer, a partial width array-type printer, or a page-width type printer. The carriage-type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge. The combined printhead and cartridge assembly is attached to a carriage that is reciprocated to print one swath of information at a time, on a stationary receiving medium, such as paper or a transparency, where each swath of information is equal to the length of a column of nozzles.
After the swath is printed, the receiving medium is stepped a distance at most equal to the height of the printed swath so that the next printed swath is contiguous or overlaps with the previously printed swath. This procedure is repeated until the entire image is printed.
In contrast, the page-width printer includes a stationary printhead having a length sufficient to print across the width or length of the sheet of receiving medium. The receiving medium is continually moved past the page-width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page width fluid ejector printer is described, for instance, in U.S. Pat. No. 5,192,959, incorporated herein by reference in its entirety.
Fluid ejection systems typically eject fluid drops based on information received from an information output device, such as a personal computer. Typically, this received information is in the form of a raster, such as, for example a full page bitmap or in the form of an image written in a page description language. The raster includes a series of scan lines comprising bits representing individual information elements. Each scan line contains information sufficient to eject a single line of fluid droplets across the receiving medium a linear fashion. For example, fluid ejecting printers can print bitmap information as received or can print an image written in the page description language once it is converted to a bitmap of pixel information.
Thermal fluid ejection systems with two heaters per ink channel can eject different sized drops based on the operation of the two heaters. Thermal fluid ejection systems can also be incorporated into a dual array roofshooter structure. The dual array roofshooter structure can utilize two heaters per ink channel. As a voltage is applied across a selected resistor of a heater, a vapor bubble grows in the associated channel and displaces ink from the channel, so that is ejected from the channel orifice as a droplet
When large sized drops are required, a drop is fired with both of the heaters operating in order to produce a large spot on the receiving medium. When a smaller sized drop is required, a drop is fired using only one of the two heaters. The larger spot creates a high productivity/low resolution pattern of the fluid droplets while the small drop produces a low productivity/high resolution pattern of the fluid droplets on the receiving medium.
Thermal fluid ejection systems with dual heaters per channel are limited, however, in their ability to create intermediate spots sizes between the largest spot size and ejecting no fluid at all. In particular, in this conventional roofshooter architecture, only three spot size levels can be obtained as only zero, one small, or one large drop can be ejected per nozzle per channel.
This invention provides a thermal fluid ejection systems with two heaters per channel while using a roofshooter structure with a dual array system to expand the spot size level capabilities.
In various exemplary embodiments of the fluid ejection systems and methods with a roofshooter structure according to this invention, the fluid ejection system includes a first array of channels with at least two heaters between the fluid supply and the end of each first array of channels and a second array of channels with at least two heaters between the fluid supply and the end of each second array of channels. Each array of channels can eject fluid drops of at least two sizes onto the receiving medium during a single pass past a single point. If the two channel arrays are aligned in the printing direction, then a given pixel on the page can receive either no drops, one small drop, two small drops, one large drop, one large drop and one small drop or two large drops during a sinlge pass, depending on how many heaters are activated in the two aligned drop ejectors.
These and other features and advantages of this invention are described and are apparent from the detailed description of various exemplary embodiments of the systems and methods according to this invention.